Glaucoma is an ophthalmic disease that leads to irreversible visual impairment. It is the fourth most common cause of blindness and the second most common cause of visual loss in the United States, and the most common cause of irreversible visual loss among African-Americans. Generally speaking, the disease is characterized by a progressive optic neuropathy caused at least in part by deleterious effects resulting from increased intraocular pressure. In normal individuals, intraocular pressures range from 12 to 20 mm Hg, averaging approximately 16 mm Hg. However, in individuals suffering from primary open angle glaucoma, intraocular pressures generally rise above 22 to 30 mm Hg. In angle closure or acute glaucoma intraocular pressure can reach as high as 70 mm Hg leading to blindness within only a few days. Interestingly, the loss of vision can result from statistically normal intraocular pressures in individuals with unusually pressure-sensitive eyes; a condition known as normotensive glaucoma. [See, e.g., P. L. Kaufman and T. W. Mittag, “Medical Therapy Of Glaucoma,” Ch. 9, Sec. II (pp. 9.7-9.30) In P. L. Kaufman and T. W. Mittag (eds.): Glaucoma (Vol. 7 of S. M. Podos and M. Yanoff (eds): Textbook of Opthalmology Series). London, Mosby-Year Book Europe Ltd. (1994); A. C. Guyton, Textbook of Medical Physiology (W. B. Saunders Co., Sixth Ed.), pp. 386-89 (1981)].
Open-angle glaucoma constitutes approximately 90% of all primary glaucomas and is characterized by abnormally high resistance to fluid (aqueous humor) drainage from the eye. Normal resistance is required to maintain an intraocular pressure sufficient to maintain the shape of the eye for optical integrity. This resistance is provided by the trabecular meshwork, a complex, multilaminar tissue consisting of specialized cells with a dense actomyosin cytoskeletal network, collagenous beams and extracellular matrix. The resistance of the trabecular meshwork normally is such that intraocular pressure is ˜16 mm Hg, a pressure at which aqueous humor leaves the eye at the same rate at which it is produced (2.5 μL/minute). In the glaucomatous eye, the rate of aqueous humor production remains constant, while it is the increased resistance to outflow that is responsible for the elevated intraocular pressure.
Typical treatments for glaucoma comprise a variety of pharmaceutical approaches for reducing intraocular pressure (IOP), each with their drawbacks. Beta-blockers and carbonic anhydrase inhibitors reduce aqueous humor production, which is needed to nourish the avascular lens and corneal endothelial cells, and the prostaglandins effect the uvealscleral outflow pathway, which only accounts for 10% of the total outflow facility. There are currently no commercially approved therapeutic agents which act directly upon the trabecular meshwork, the site of aqueous humor drainage where increased resistance to aqueous humor outflow is responsible for elevated IOP. Therefore, a medical need remains for improved IOP-lowering medications that target this structure. Pharmacological agents which target the trabecular meshwork may provide relief to the significant numbers of patients that do not respond adequately to current IOP-lowering medications and/or cannot tolerate the side effects associated with these agents. Additionally, these molecules may prove beneficial as adjunctive therapy in combination with other classes of IOP-lowering medications.
U.S. Pat. Nos. 6,586,425, 6,110,912, and 5,798,380 disclose a method for the treatment of glaucoma using compounds that affect the actin filament integrity of the eye to enhance aqueous humor outflow. These patents also specifically disclose kinase inhibitors as well as latrunculin-A, latrunculin-B, swinholide-A, and jasplakinolide, which cause a perturbation of the actin cytoskeleton and tight junctional complexes in the trabecular meshwork or the modulation of its interactions with the underlying membrane. Perturbation of the cytoskeleton and the associated adhesions reduces the resistance of aqueous humor flow through the trabecular meshwork and thereby reduces intraocular pressure.
Wound healing is another approach in which these classes of molecules can aid in modulating IOP. Trabeculectomy is the most common form of glaucoma filtration surgery and remains as the first-line therapy for surgical reduction of pharmacologically uncontrolled intraocular pressure in primary open angle glaucoma. This procedure establishes a limbal fistula through which aqueous humor drains into the subconjunctival space establishing a filtering bleb to lower intraocular pressure. The success of the procedure is highly dependent on pharmacological modulation/inhibition of wound healing.
A major advance in the surgical management of glaucoma has been the use of antimetabolites to prevent scarring after glaucoma filtration surgery. Postoperative scarring of the filtering bleb is the most crucial factor in determining the short and long-term outcome of modern glaucoma filtration surgery. The antimetabolites mitomycin C (MMC) and 5-fluorouracil (5-FU) are widely used to suppress scarring and thus failure of the filtering bleb. In a large retrospective study, conventionally performed trabeculectomy has shown a failure rate of up to 30% within 3 months after surgery. To lower the incidence of this detrimental complication, various methods have been investigated in order to avoid scarring of the filtering bleb, mostly dealing with the intraoperative or postoperative application of antimetabolic drugs
Despite their positive long-term effect on prolonged filtration, the application of cytotoxic drugs to a surgically opened eye increases the incidence of severe complications such as concomitant increases in vision threatening complications. MMC exhibits a high incidence of severe post-application complications, as does 5-FU; although its side effects mainly affect the corneal epithelium its clinical use is limited by severe pain and discomfort to the patient. No sufficient method has been established to achieve satisfying postoperative long-term surgical results with only minimal or no side effects for the patient.
There exists a need for effective and cost-practical cytoskeletal active compounds to treat glaucoma, to modulate wound healing after trabeculectomy, and to treat other diseases or disorders that are affected by the integrity of the actin cytoskeleton. ROCK inhibitors impact diverse physiological functions associated with cytoskeletal rearrangement leading to changes in cell morphology, cell contractility, cell motility and cytokinesis. They play a key role in modulating focal adhesion and stress fiber formation in trabecular meshwork cells which express a dense, dynamic cytoskeletal network. Thus, altering the contractility of these cells leads to drainage-surface expansion of the trabecular meshwork and Schlemm's canal. Additionally, loss of cell-substratum adhesions may influence paracellular fluid flow across Schlemm's canal or alter the fluid flow pathway through the juxtacanalicular tissue of the trabecular meshwork. Both are likely the basis for intraocular pressure-lowering effect of ROCK inhibitors. Thus, there exists a need for novel cytoskeletal active compounds that can be obtained using practical synthetic procedures.